In a cellular communication network, mobile devices (also known as User Equipment (UE) or mobile terminals, such as mobile telephones) communicate with remote servers or with other mobile devices via base stations. An LTE base station is also known as an ‘enhanced NodeB’ (eNB), which is coupled to an LTE core network also known as an Enhanced Packet Core (EPC) network.
In their communication with each other, LTE mobile devices and base stations use licensed radio frequencies, which are typically divided into frequency bands and/or time blocks. Depending on various criteria (such as the amount of data to be transmitted, radio technologies supported by the mobile device, expected quality of service, subscription settings, etc.), each base station is responsible for controlling the transmission timings, frequencies, transmission powers, modulations, etc. employed by the mobile devices attached to the base station. In order to minimise disruption to the service and to maximise utilisation of the available bandwidth, the base stations continuously adjust their own transmission power and also that of the mobile devices. Base stations also assign frequency bands and/or time slots to mobile devices, and also select and enforce the appropriate transmission technology to be used between the base stations and the attached mobile devices. By doing so, base stations also reduce or eliminate any harmful interference caused by mobile devices to each other or to the base stations.
Current mobile devices typically support multiple radio technologies, not only LTE. The mobile devices might include, for example, transceivers and/or receivers operating in the Industrial, Scientific and Medical (ISM) radio bands, such as Bluetooth or Wi-Fi transceivers. The term ‘Bluetooth’ refers to the standards developed by the Bluetooth Special Interest Group, and the term ‘Wi-Fi’ refers to the 802.11 family of standards developed by the Institute of Electrical and Electronics Engineers (IEEE). If such a non-LTE communication technology is supported, instead of communicating via LTE base stations, mobile devices may also communicate with remote servers or with other mobile devices using non-LTE communication means, e.g. using an appropriate ISM communication technology. For example, the mobile devices may communicate via an access point (e.g. a Wi-Fi AP) operating in accordance with the 802.11 family of standards by the Institute of Electrical and Electronics Engineers (IEEE).
Recently, a so-called ‘dual mode’ base station has been introduced comprising an LTE home base station (HeNB) part (e.g. a pico/femto base station or other low-power node) and a non-LTE access point part (e.g. a Wi-Fi AP). Such a combined HeNB/AP base station may also sometimes be referred to as a dual mode femto access point (FAP) or dual FAP.
ISM and other radio technologies (hereafter commonly referred to as non-LTE technologies) use frequency bands close to or partially overlapping with the LTE frequency bands, as illustrated in FIG. 12. Some of these non-LTE frequency bands are licensed for a particular use (e.g. Global Positioning Systems (GPS) bands) or might be unlicensed bands and can be used by a number of radio technologies (such as Bluetooth and Wi-Fi standards using the same range of ISM frequency bands). The manner in which these non-LTE frequency bands are used are, therefore, not covered by the LTE standards and are not controlled by the LTE base stations (e.g. a HeNB of a dual FAP). However, transmissions in the non-LTE frequency bands might, nevertheless, still cause undesired interference to (or suffer undesired interference resulting from) transmissions in the LTE bands, particularly in the overlapping or neighbouring frequency bands.
In particular, such undesired interference may be experienced between LTE and non-LTE (ISM) radio communications in at least the following scenarios:                LTE Band 40/41 radio transmitter causing interference to ISM radio receiver;        ISM radio transmitter causing interference to LTE Band 40/41 radio receiver;        LTE Band 7 radio transmitter causing interference to ISM radio receiver;        ISM radio transmitter causing interference to LTE Band 7 radio receiver; and        LTE Band 7/13/14 radio transmitter causing interference to GPS radio receiver.        
When such undesired interference arises as a result of communication occurring concurrently in the same mobile device or in the same base station (for example, as a result of concurrent use of LTE and non-LTE radio technologies) the interference is sometimes referred to as ‘in-device coexistence (IDC) interference’ which causes an ‘in-device coexistence (IDC) situation’.
In order to be able to alleviate the problems due to IDC interference, the mobile device may be configured to attempt to address such IDC problems on its own and, if the mobile device cannot solve the problem on its own, with the assistance of its serving base station. For example, an IDC problem may be addressed by the base station selecting a different frequency (FDM solution) for the mobile device, by reconfiguring its transmissions (e.g. apply discontinuous reception (DRX) and/or change its subframe pattern) (TDM solution), and/or by adjusting the base station's (and/or the mobile device's) transmission power (Power Control solution).
The inventors have realised that difficulties may arise in simultaneously operating both the LTE and non-LTE parts of such dual FAPs due to the potentially severe interference experienced in some of the (neighbouring or overlapping) frequency bands used by both the LTE and the non-LTE communication technologies.
Such difficulties are particularly likely to occur with respect to dual FAPs implementing both an LTE base station and a non-LTE access point as part of the same network node. In this case, the above (FDM/TDM/Power Control) solutions are not always applicable because any change in the operation of the LTE base station (of the dual FAP) may still cause (or continue to cause) unexpected interference for communications using the access point part of the dual FAP.
The inventors have also realised that whilst it is possible to co-ordinate some of the operations of LTE base stations and other base stations operating in accordance with an earlier standard from which LTE has been derived, e.g. due to the inherent backward compatibility between such related standards, it is particularly difficult to ensure optimal communication characteristics (e.g. signal quality, error rate, interference level) for dual FAPs implementing both an LTE base station and a non-LTE access point because of the differences between the operation of the LTE and the non-LTE parts.